Q: Big fan never comes on. If I run the AC, the smaller fan comes on.

Hello, thanks for writing in. If the fan never comes on then the circuit needs to be tested. This can be caused by the wiring or by the fan itself. I usually start by testing the fan with an ohm meter. If the reading is off then the fan needs to be replaced. If the fan is fine then the circuit needs to be tested to see if the fan is losing voltage. If it is then it may have a blown fuse or it may have a relay or computer issue. If you want to have this looked at or repaired, consider YourMechanic, as a certified mechanic can come to your home or office to inspect the issue for you and make or suggest any repairs.